def f(n):
    a, b = 0, 1
    if n < 0:
        return None
    elif n == 0:
        return a
    elif n == 1:
        return b
    for i in range(n // 2):
        a = a + b
        b = a + b
    if n % 2 == 0:
        return a
    else:
        return b


if __name__ == '__main__':

    def main():
        for i in range(10):
            print(i, f(i))

    main()
